1. Technical Field
The present disclosure relates to an optical inner-surface measurement device.
2. Description of the Related Art
Power performance and a fuel consumption efficiency of an automobile are largely affected by, e.g., qualities of a finished dimension and a geometric accuracy of a cylinder of an automobile engine. These qualities are generally inspected by use of a contact-type measuring device such as a roundness measuring instrument, a surface roughness tester, and a length measuring machine including a linear scale. Recently, however, in order to perform the inspection without damaging a measurement object (an object to be measured), an optical non-contact-type measuring device has been proposed.
One example of a technique for observing and inspecting the presence or absence of a damage on an inner surface of a measurement object in a non-contact manner is a diagnostic imaging technique (optical imaging technique). This technique is widely used for purposes such as inspection of various mechanical parts, devices, and equipment in sites such as a medical site. For example, in a manufacturing site for, e.g., precision equipment, the inspection and the diagnostic imaging with respect to a deepest part of a deep hole may be performed by camera observation with a general endoscope. Alternatively to the camera observation, an automatic inspection as below may be employed. That is, according to the automatic inspection, an inspection object (an object to be inspected) is irradiated with a light beam, strength of reflected light is detected by an optical sensor, and determination by a computer is executed.
Meanwhile, in a medical field, various techniques are researched and used to observe a diseased part inside a human body. The various techniques encompass X-ray computed tomography, nuclear magnetic resonance, and OCT imaging (optical coherence tomography) by an endoscope, which makes use of optical coherency. Each of these techniques enables observation of a tomographic image.
In some cases, the above measurement device may employ near-infrared light, which is used as a light source in the medical field. In this arrangement, in a case where the measurement object has a deep hole having an inner peripheral surface made from metal, near-infrared light is reflected by the inner peripheral surface. Meanwhile, in a case where the inner peripheral surface made from metal includes a resin-film layer formed thereon, near-infrared light is semi-transmitted through the resin. Thus, simultaneously with observation of a three-dimensional shape of the inner peripheral surface, it is possible to perform measurement of a thickness accuracy of the resin film and observation of a pinhole on the resin surface.
For example, JP-A-08-233545, JP-A-05-180627, and JP-A-2010-236870 disclose representative structures of an observation device employing the technique for observing or measuring an inner peripheral surface of a mechanical part by irradiating the inner peripheral surface with a light beam.
FIGS. 1 to 4 each show an optical probe of a known optical inner-surface measurement device. In a probe 11 shown in FIGS. 1 to 4, a rotational optical fiber 1 is supported by bearings 5a and 5b inside a tube 3. Inside a probe case 6, the rotational optical fiber 1 is rotated by a fiber-rotating motor 10, pulleys 7 and 8, and a belt 9. Consequently, a mirror 2 with a hemispherical lens is rotated. The mirror 2 with the hemispherical lens is attached to a forward-end of the rotational optical fiber 1. A light beam is guided through the rotational optical fiber 1, and is emitted from the mirror 2 with the hemispherical lens. The light beam is then transmitted through a light-transmitting member, and is emitted to an inspection object 100a. A reflected light from the inspection object 100a is guided to the rotational optical fiber 1 again. In this manner, a roundness is measured.
In a state shown in FIG. 1, a hole of the inspection object 100a is favorably set at a right angle with respect to a light beam to be emitted, rather than at an inclined angle. Consequently, d1 and d2 shown in FIG. 2 are measured correctly, and thus a roundness is also indicated correctly.
Meanwhile, in a state shown in FIG. 3, a hole of an inspection object 100b is set at an inclined angle with respect to a light beam to be emitted. Consequently, as shown in FIG. 4, a measured length dx is longer than an actual length, and thus a roundness cannot be measured correctly, either.